Optical components such as touch panels and various displays which become in contact with finger or which are operated by hand are inherently associated with the problem of visibility loss since surface of such component is easily contaminated by the oil from human body. In order to reliably maintain the components in good working order, the surface of such component is strongly demanded to have an improved smudge proof property. Silicone compounds as typically represented by dimethyl silicone oil are known to provide excellent water repellency and lubricity with the surface on which they are applied. Silicone compounds, however, are inferior in their ability of reducing surface tension compared to fluorine compounds, and accordingly, their oil repellency has been insufficient and their smudge proof property against the oil has been incomplete. In view of such situation, fluorine compounds having superior oil repellency have often been used for such purpose.
Various attempts have been made to provide an article with improved smudge proof properties including smudge resisting property, easy smudge removal, and fingerprint resisting property by applying a fluorine-containing compound on the surface of the substrate to thereby form a film having improved water and oil repellency. In such case, a fluorinated alkyl-substituted silane or a fluorinated polyether-substituted silane has been deposited on the surface of a substrate or a substrate having a protective film by vapor deposition to thereby provide the surface with water and oil repellency. When this method is adopted, the resulting smudge poof layer is a thin layer comprising oriented monomolecules, and such film has excellent smudge proof property. However, vapor deposition requires expensive installation, which is economically disadvantageous. Moreover, when a transparent plastic optical component is treated, a protective film should be formed beforehand as a countermeasure for improving the inferior scratch resistance inherent to the plastic article, and such two step method is disadvantageous in economic point of view. The situation is similar in the case of forming a thin layer of the silane hydrolysate since formation of an evenly coated monomolecular film is also difficult, and a two-step treatment with the preliminary formation of protective film is also required.
Use of a silicone resin prepared by hydrolysis of a silane compound having a fluorine-containing organic group or a mixture of such silane compound having a fluorine-containing organic group with another silane compound for the coating agent has also been proposed (see JP-A 2002-53804 (Patent Document 1)). While this method is capable of forming a film having excellent smudge proof property, the resin contains a large amount of fluorine-containing organic substituent which is not crosslinkable and which is also bulky, and the resulting film has low crosslink density, and the scratch resistance does not reach the level required for such film. In other words, the film does not reach the level that all properties required for an optical component are provided by such film, namely, by only one treatment.
In order to improve the scratch resistance, JP-A 2000-119634 (Patent Document 2) proposes a method in which a perfluoroalkyl group-containing silane is simultaneously hydrolyzed with various silane compounds such as tetraalkoxysilane; JP-B 6-29332 (Patent Document 3) proposes a method in which a perfluoroalkyl group-containing silane is used with a bissilane compound containing a perfluoroalkylene group as a spacer, and a tetraalkoxysilane; and Japanese Patent No. 2629813 (Patent Document 4) proposes a method in which a bissilane compound containing a perfluoroalkylene group as a spacer is used with an epoxy functional silane. Although these methods have realized the intended scratch resistance and adhesion at a relatively high level, the resulting film had various drawbacks in the actual use due to the reduced fluorine content. More specifically, the concentration of the fluorine-containing substituent was not higher at the surface, and as a consequence, the film was insufficient in the smudge proof property, and also, in the resistance to chemicals such as household detergent, and in particular, in the resistance to alkalis.
As described above, there has been no system capable of providing the scratch resistance which is deficient in the plastic material, the smudge resistance including the resistance to oily components from the human body, and the resistance to alkaline household detergent which is used in washing optical components in only one coating step on the plastic substrate.